The present invention relates to press drives. More particularly, the present invention relates to a single speed, hydraulic actuated press drive which utilizes an oil shear clutch unit, an oil shear brake unit and a single piece hydraulically actuated actuator which simultaneously operates both the clutch unit and the brake unit.
Press drives having dry friction clutch/brake units depend on the rubbing of a dry friction material against dry reaction members to start and stop the press. This dry friction rubbing causes wear of both the friction material and the reaction members as well as the generation of heat. The faster the press operates and/or the faster the flywheel rotates, the greater the wear and heat generated. This generation of wear and heat requires periodic gap adjustments between the dry friction material and the dry reaction members to keep the press operating correctly.
Some dry friction clutch units and brake units in press drives are mechanically interlocked. Mechanical interlocking of the dry friction clutch and the brake units means that a single piston first releases the brake and then engages the clutch for starting of the press. For stopping the press, the clutch is first released and then the brake is applied by the piston. These mechanically interlocked units have a significant portion of the mass of the clutch and brake units mounted on the drive shaft and this can represent as much as 80% of the total inertial of the press that the press drive must stop and start. Mechanical interlocking of the dry friction clutch and brake units reduces the frequency required for gap adjustments because the two units are never simultaneously engaged, but mechanical interlocking does not eliminate this adjustment procedure. Adjustment for these dry friction units is still necessary when the gap has increased to the point that the response of the press is adversely affected.
Press drive builders have introduced lower inertia clutch and brake designs in an effort to reduce the start-stop inertia and thus increase the useful life of these drives. These low inertia designs typically require separate pistons to release the brake and engage the clutch. The start-stop inertia with these designs has been reduced to approximately 60% of the total inertia. In order for the press drive to function correctly, the separate pistons must be properly synchronized to prevent overlap of the clutch and brake units. When the clutch starts to engage before the brake is fully released, or, when the brake starts engaging before the clutch is fully disengaged, excessive heat is generated and wear of the friction material and the reaction member is greatly increased. Conversely, if there is too much time between the engage/release of the clutch/brake, drifting occurs resulting in sluggish operation and if the drift is high enough, it can result in unsafe operation of the press.
In addition to the issues discussed above, the trip rate for a press equipped with a dry friction clutch/brake unit in the press drive is limited because the mass of the unit determines its heat capacity. If the mass is increased to increase its heat capacity, the inertia that must be stopped and started is increased. These two factors define a closed loop from which it is impossible to escape when trying to increase the performance of the system.
The continued development of press drives includes the development of clutch and brake units which address the problems associated with dry friction clutch and brake units, the high inertia associated with clutch and brake units and the synchronization for the operation of the clutch and brake units.
The present invention provides the art with a press drive system which uses oil shear brake and clutch drives. The entire system uses hydraulic actuation instead of air actuation. The clutch and brake units are arranged axially along the output shaft to minimize the outer size of the unit and thus reduce the inertia of the system. The clutch and brake units are mechanically interlocked using a single piece piston that moves in response to the presence of pressurized hydraulic fluid.
The oil shear design for the clutch and brake units offers the advantage of little or no wear for the friction material and the reaction members. In addition, the oil shear design does not have the problem of brake fade. This provides a more precise operation of the press and dramatically increases press up-time. The oil film within these oil shear units carries the heat generated by start-stops away from the friction material and the reaction members. This removal of heat offers the advantage that there is now no practical limit for the press trip rate and flywheel speed, plus it provides unlimited inching capabilities.
The clutch and brake units of the present invention utilize a disc stack of multiple discs. These multiple disc surfaces can be used to greatly reduce the clutch/brake inertia thereby allowing the mechanical interlocking of the clutch and brake units without inertia penalty. In addition, the axial positioning of these two units also helps in the reduction of the clutch/brake inertia.
Finally, the mechanical interlocking of the clutch and brake units completely eliminates the need for any gap adjustment since the friction material and the reaction members experience little or no wear.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.